How do you make all dataframes in a list have the same number of columns?

I’m trying to make all dataframes in a list have the same number of columns.

Create a list of 3 dataframes, but the 2nd has 1 extra column.

    my_data<- 
        list(    data.frame(
         V1= c(1,1,1,1,1),
         V2= c(2,2,2,2,2),
         V3= c(3,3,3,3,3),
         V4= c(4,4,4,4,4),
         V5= c(5,5,5,5,5)), 
       data.frame(
         V1= c(1,1,1,1,1),
         V2= c(2,2,2,2,2),
         V3= c(3,3,3,3,3),
         V4= c(4,4,4,4,4),
         V5= c(5,5,5,5,5),
         V6= c(6,6,6,6,6)),
       data.frame(
         V1= c(1,1,1,1,1),
         V2= c(2,2,2,2,2),
         V3= c(3,3,3,3,3),
         V4= c(4,4,4,4,4),
         V5= c(5,5,5,5,5))

manual removal of column: if df[[2]] has > 5 columns, remove the 6th

if (ncol(my_data[[2]])>5) {
my_data[[2]][,-6]
}

But why doesn’t the same logic doesn’t work when looping it through the list?

for (i in 1:length(my_data)) {

 if (ncol(my_data[[i]])>5) {
my_data[[i]][,-6]
 } 
}

>Solution :

Your logic works just fine. When you are iterating through the loop, you have to assign the updated frame back to that element of the list.

Simply replace:

my_data[[i]][,-6]

with

my_data[[i]]<-my_data[[i]][,-6]

within the if clause.